Evidence exists to support the theory that specific microbial combinations are present in diseases that produce symptoms such as pain and or swelling. The purpose of this study was to delineate growth profiles of potential endodontic pathogens and the development of microbial communities in mixed batch cultures. The microorganisms used in this study were Fusobacterium nucleatum ATCC 25586, Peptostreptococcus micros ATCC 33270 and Porphyromonas endodontalis ATCC 35406. Anaerobic primary cultures were obtained for the organisms in their respective media, whereas the coculturing of the three organisms was achieved in prereduced Trypticase- yeast extract-cysteine medium supplemented with 0.0005% hemin and 0.001% menadione. The secondary culture remained in an anaerobic environment (85% N2, 10% H2, 5% CO2) during growth and sampling periods. At different increments of time, samples was taken from the anaerobic mixed culture, diluted and plated with a Spiral Plating system on selective agar medias defined for isolation of each organism. Numbers of viable cells were determined from colony counts following the standard Spiral System methodology. Porphyromonas endodontalis exhibited marked growth inhibition with decreases occurring after approx. 20 hrs. Peptostreptococcus micros exhibited an initial decrease in numbers up to 20 hours, with rapid growth thereafter. Fusobacterium nucleatum's growth was unaltered in mixed culture. These studies suggest production of stimulatory and/or inhibitory factors are produced by specific bacteria in mixed culture. KEY WORDS: mixed culture, growth factors